This invention relates to the production of titanium-containing compositions suitable for use as transition metal components of Ziegler catalysts. More specifically, the invention relates to a process for producing Ziegler type catalyst components for polymerization of .alpha.-olefins of remarkably high stereoregularity or crystallinity and polymerization activity by processing solid components containing magnesium halides, electron donor compounds, and titanium compounds.
In the prior art, Ziegler catalysts have been known as catalysts for .alpha.-olefin stereospecific polymerization. Furthermore, for the purpose of further improving the activity and stereoregulating capability of these catalysts, various methods have been proposed.
Among these various improved methods, the process of producing a solid catalyst component wherein a Ziegler catalyst transition metal catalyst component is caused to contain therein a magnesium compound (as disclosed in Japanese Patent Publication Nos. 41676/1972 and 46269/1972) markedly improves the catalyst particularly with respect to its activity. These methods, however, have been proposed principally for producing high activity catalysts for polymerization of ethylene, and, while their activity is of extremely high value when they are used as catalysts for polymerization of .alpha.-olefins such as propylene, the stereoregularity of the resulting polymer conversely decreases to a remarkable degree, whereby their practical value as catalysts for stereospecific polymerization of .alpha.-olefins is greatly impaired, as is also known.
Accordingly, various methods of improving the stereo-regularity of the polymers formed in the polymerization of .alpha.-olefins in which transition metal solid catalyst components of Ziegler catalysts containing a magnesium compound are used have been proposed (e.g., in the specifications of Japanese Patent Laid Open Nos. 9342/1972, 12659/1975, and 57789/1976). A common characteristic of these methods is that an electron donor compound such as an amine or an ester is caused to be contained in the Ziegler solid catalyst component containing a titanium compound and a magnesium halide compound.
In addition, as is known through disclosures such as the specifications of Japanese Patent Laid Open Nos. 16986/1973, 16987/1973, and 16988/1973, methods of causing both the transition metal catalyst component and the trialkylaluminum component to be combined therewith to form a Ziegler catalyst to contain an electron donor compound (by addition and complex formation or like method) have also been proposed. By causing the Ziegler catalyst component containing a magnesium halide compound in its transition metal catalyst component to contain an electron donor compound, the stereoregularity of the polymer thus formed is considerably improved.
However, the stereoregularities of the polymers produced by the above described various methods are still inadequate. Accordingly, in order to obtain a polymer having the physical properties of a polymer in market demand, it becomes necessary to remove the atactic polymers from the .alpha.-olefin polymers obtained by these catalyst systems, and this necessity is one cause of the complexity of the polymer production process.
Furthermore, there are some catalyst systems which, while having high activity per titanium atom, do not necessarily have high activity per solid catalyst component, and on this point, also, improvement is desired.